Image processing apparatus

Abstract

In an image processing apparatus of the invention, HVC conversion is performed stably. THat is, an image sensor reads image data of red, green and blue of a document, while a memory stores brightness data V of a color patch. When the image data are converted to a brightness data V and color difference data WR and WB, coefficients used in the conversion of the HVC conversion are calculated by an operator based on the image data of red, green and blue of the color patch read by the image sensor and the brightness data V stored in the memory.

What is claimed is: 
     
       1. An image processing apparatus comprising: a read means for reading document image data of red, green and blue of a document and for reading patch image data of red, green and blue of a color patch;   a memory which stores a patch brightness data V of the color patch;   an HVC converter which converts the document image data to an image brightness data V 2  and color difference data by means of coefficients; and   an operator which calculates the coefficients based on the patch image data of red, green and blue of the color patch read by said read means and the patch brightness data V stored in said memory.   
     
     
       2. The apparatus according to claim 1, wherein the coefficients comprises two coefficients "a 1  ", and "a 2  ", wherein the color difference data comprises WR and WB, and said HVC converter converts the image data of red R, green G and blue B to the image brightness data V 2  and the color difference data WR and WB with the use of coefficients a 1  and a 2  so that   V.sup.2 =a.sub.1 ·R+a.sub.2 ·G+(1-a.sub.1 -a.sub.2)·B,       WR=(R-V.sup.2)/(1-a.sub.1),     and     WB=(B-V.sup.2)/(a.sub.1 +a.sub.2).     
     
     
       3. The apparatus according to claim 1, wherein said HVC converter calculates chroma signal W as follows:   W=(WR.sup.2 +WB.sup.2).sup.1/2.     
     
     
       4. An image processing apparatus comprising: a read means for reading document image data of red, green and blue of a document;   a memory device storing patch brightness data V of a color patch;   an HVC converter which converts the image data to an image brightness data V2 and color difference data WR and WB by means of coefficients;   a first operation means for determining a part of the coefficients for the conversion performed by said HVC converter by using patch image data of red, green and blue obtained by said read means and the patch brightness data V stored in said memory device; and   a second operation means for determining a remainder of the coefficients via a predetermined relation between the coefficients.   
     
     
       5. An image processing apparatus comprising: a read means for reading document image data of red, green and blue of a document;   a memory device storing patch brightness data V of a color patch;   an HVC converter which converts the image data to an image brightness data V 2  and color difference data WR and WB by means of coefficients;   an operation means for determining the coefficients necessary for the conversion performed by said HVC converter by using patch image data of red, green and blue obtained by reading the color patch by said read means and the patch brightness data V stored in said memory device;   a start means for instructing staff of document reading by said read means;   a setting means for setting an adjustment mode; and   a controller which outputs image data of the image brightness data V 2  and the color difference data WR and WB obtained by said HVC converter by means of predetermined coefficients if the adjustment mode is not set by said setting means when said start means instructs start of document reading, said controller activates said operation means in order to determine the coefficients if the adjustment mode is set by said setting means when said staff means instructs start of document reading.